1. Field of the Invention
This invention relates generally to compressors wherein compressor discharge pressure is proportional to compressor rotor speed and, more particularly, to bleed valves for avoiding surge in such compressors.
2. Description of Prior Art
Because engine performance limiting compressor surge in gas turbine engines is advantageously avoided by selectively bleeding compressed air, many automatic bleed valves have been proposed. In one pertinent valve compressor bleed as a function of compressor pressure ratio is effected by a bleed control poppet, the position of which is determined by a diaphragm exposed on one side to a control pressure proportional to compressor discharge pressure and on the other side to atmospheric pressure. In another pertinent valve where compressor bleed is primarily a function of compressor pressure ratio, a secondary control element is operative to initiate compressor bleed as a function of the rate of increase of compressor discharge pressure in the event that compressor output is blocked. A bleed valve according to this invention schedules compressor bleed as a function of compressor rotor acceleration during periods of rotor acceleration and also initiates compressor bleed for a predetermined period after the onset of rotor deceleration to condition the compressor for surge-free operation in the event of rapid reacceleration of the compressor rotor.